A distortion corrected passive RC noise shaping ADC for biomedical applications

High-resolution noise shaping ADCs are increasingly used in measurement of biopotential signals. This paper presents a novel low power low voltage ADC based on a Dual-Slope (DS) integrating quantizer. To reduce power consumption, the active RC integrator used in integrating quantizers has been replaced by a passive RC low pass filter. Hence, no operational amplifiers are needed. This simplification implies two drawbacks. The passive integrator limits noise shaping due to imperfect integration. Moreover, approximation of linear ramps by an exponential capacitor charge introduces distortion. This paper reveals that the most limiting factor is distortion instead of imperfect integration. A simple method is proposed to compensate the distortion.